This invention relates to electrical induction motors and particularly to means for inducing internal unbalanced forces on the rotors of motors for damping and counteracting external forces on the motor rotors or shafts.
Ideal electrical induction motors develop mechanical torque only, i.e., balanced rotating tangential forces tending only to cause rotation of the motor rotor. All other forces, namely transverse and longitudinal forces on the motor rotor, are zero. This results from geometrical and axial symmetry of the rotor, air gap and magnetic fluxes. Radial forces exist, but they are balanced and cause only internal stress in the rotor. Accordingly, with proper design, ideal motor rotors rotate perfectly smoothly with no mechanical vibrations in any direction.
Matters change, however, when the motor rotors are connected for doing work. In milling machines, for example, vibration forces are generated during the cutting process which can deteriorate the surface of the workpiece and increase the roughness of the cut surface. Additionally, these vibrations can induce corresponding vibrations in the motor rotor, thereby causing wear of the motor bearings. The present invention is directed to the problem of reducing externally caused vibrations.